1. Field of the Invention
The present invention relates to an upper structure of an engine, and primarily to an arrangement structure of an ignition system.
2. Description of the Background Art
As an ignition coil adapted to be used for generating sparks from a spark plug of an engine, a stick-type ignition coil unit is widely employed which is capable of being inserted into a plug hole in a cylinder head from above a head cover of an engine. This type of ignition coil unit has a head portion which is exposed above the head cover and provided with a connector adapted to allow an electric wire to be connected thereto. Thus, an operation of connecting the electric wire to the connector and replacing the ignition coil unit with a new one can be performed without detaching the head cover. As one of the engine combustion control techniques, a multi-point ignition engine equipped with a plurality of spark plugs per cylinder has been proposed (see, for example, JP 2001-234842A).
In the multi-point ignition engine having an ignition coil unit for each spark plug, the number of ignition coil units will multiplicatively increase. Consequently, an area on a head cover to be occupied by head portions of ignition coil units becomes larger to cause difficulty in ensuring a space for arranging other component, such as an oil filler section, and deterioration of flexibility in design of the head cover.